Concentration's intended use is to negate a negative status effect or displacement that is inflicted by the enemy.

Deorbit is meant to pull the player back so that they can be withdrawn from damage (melee damage at the least) and allow the AST to catch up with healing, or pull the player from a bad position, etc. This is an unconventional CD when compared to the other two healers, who's CDs are direct healing and damage mitigation.

Imagine of Concentrate canceled the effect of Divine Benison or or Lustrate. That would be pretty frustrating for both players:
-The Player using Concentrate will not be able to block the enemy CC that they were intending for
-The Healer has now wasted a CD that had no effect in minimizing damage/allow them to catch up on healing.

Like it was previously mentioned, due to the kits of all three healers, WHM and SCH do not suffer the loss of a CD, so therefore they don't need to gamble unlike the AST.

Deorbit is not like Fluid Aura or Aura Blast. Those two CDs are intended to knock an ENEMY player away from themselves. Deorbit is meant for a TEAMMATE player who may be in danger. They are both displacements in that respect, but they serve two different purposes. Basically at this point you're pretty much saying "Hey AST tough titties for Deorbit + Concentrate"